The present invention relates to conveyors equipped with article-conveying driven rollers, and more particularly to those equipped with means for altering the amount of thrust exerted on the articles being conveyed.
In those areas of a production line where the need to control the movement of articles is greatest, conveyors equipped with driven rollers are frequently preferred over those equipped with article-engaging endless belts. Such driven rollers are relatively closely spaced, small diameter assemblies and are often found in canning, bottling, pharmaceutical and electronic assembly plants. Typically, these so-called mini-roller conveyors are modular and may be arranged in a wide variety of configurations so that the direction of travel of the articles can be altered relatively easily.
At various stages in the production line, the products or product containers accumulate on the conveying apparatus. For instance, where one automated process takes longer to perform than the previous upstream operation, the containers and/or goods accumulate on the conveyor at or near the slower downstream operation. Such accumulations may also occur within the conveyor assembly where the direction of travel changes or where the articles must be channelled through narrower passages. The resulting congestion creates pressure against the walls of the containers, such as cans or bottles, as the upstream items are forced against those moving at a slower rate or not at all. Such pressure tends to damage the articles and increase the wear and tear on the conveying apparatus. While the initial vector of this force is substantially coplanar with the would-be direction of travel of the articles, it builds and spreads quickly, creating excessive friction and drag in the moving conveyor parts as the number of articles accumulating in a given area increases.
Such accumulation pressure may be reduced in a number of ways. For instance, the articles may be diverted to an accumulation table and then shifted on demand to the downstream equipment. Alternatively, additional units of processing equipment may be provided, and the articles conveyed in separate streams to the duplicate machinery. Accumulation pressures may also be lowered by regulating the speed and time it takes them to reach the downstream machinery. However, in each case, substantial additional manufacturing costs are incurred.
Another response has been to limit the ability of the rollers to grip the undersurface of the articles being conveyed. This reduction in friction or surface contact permits the articles and rollers to slip relative to one another when an accumulation of items overloads the system. One means of providing this slippage may include providing the roller surfaces with material having a relatively low coefficient of friction, such as lubricants, and/or by forming the rollers from relatively hard and smooth materials such as stainless steel. Another method may be to limit the amount of surface contact between the rollers and the articles being conveyed, such as by employing containers whose undersurface is concave or otherwise varied.
Another method of providing this slipping effect has been to provide one or more oversized transport sleeves on each roller shaft, wherein the inner diameter of the sleeve is greater than the outer diameter of the shaft. In this manner, the shafts continue to rotate when congestion limits the movement of the articles being conveyed, while the oversized sleeves in contact with the congested articles remain relatively stationary.
Another, and closely related, problem with conventional mini-roller conveyors has involved the means of transferring power from an electrically actuated drive motor to the roller shafts. In one instance, each of a plurality of roller shafts was connected to a planetary gear transmission by means of a flexible drive shaft. See, U.S. Pat. No. 4,313,536. A clutch mechanism was provided between each of the transmissions and the drive motor so that in certain conditions, such as heavy congestion, power would not reach the transmission. This clutch mechanism added to the already complex mechanical structure. In addition, the torque applied to the roller shafts was limited to that which could be applied at one end thereof.
In another instance, an elastomeric belt was provided between each transversely disposed roller shaft and an underlying, longitudinally extending drive shaft. While mechanically relatively simple, the downwardly extending belts pulled the roller shafts in that direction, thereby augmenting the wear on the roller shaft bearings already subject to the weight of the conveyed articles.
In addition to the above mentioned drive systems, conveyors equipped with article-engaging rollers have also been driven by endless belts. Such conveyors, however, were used in moving large boxes and pallets of goods and were provided with relatively large diameter rollers. Elaborate mechanisms were provided to regulate overload conditions, accompanied by relatively high cost and various maintenance problems.
Thus, the present inventor was faced with several problems which have plagued mini-roller conveyors in the past. First, there were the problems of devising a conveyor that was relatively simple mechanically and adaptable to a wide variety of shapes and sizes. Second, the problem of handling overload conditions without damaging the goods or the internal mechanisms of the conveyor also needed a solution. Third, there was the problem of devising a mini-roller conveyor to sufficiently close tolerances that the cans, bottles or other articles intended to be conveyed thereon would have a smooth, even surface upon which to travel.